AQA · OCR A · acid–base and redox
Back titration question generator
Learn the calculation method, then practise with original exam-style questions. Each question includes marks, clues and a worked mark scheme.
Learn the method, then try exam mode
Start with the straightforward generator to learn the calculation sequence. Exam mode changes the context, data presentation and number of stages. Year 13 students can also select redox questions.
The generator starts from a valid hidden answer and works backwards to the question data. The questions are original and are not copied from exam papers.
Foundation practice
See the calculation structure clearly
The first questions use manageable numbers. Each clue follows the calculation order.
Give your answer to three significant figures.
Original generated questions
Practise the way the calculation appears in an exam
Equations, tables and the amount of scaffolding vary with the selected level.
Printable practice
Create an original mini exam
Questions print first; the mark scheme starts on a separate page.
How to solve a back titration
- Find the amount initially added. Convert volume from cm³ to dm³ and use n = cV.
- Use the later titration to find the amount left over. Apply the equation for the second reaction carefully.
- Scale up when only part of a diluted solution was titrated. For example, results from 25.0 cm³ of a 250 cm³ solution must be multiplied by 10.
- Subtract. Initial amount minus amount left over gives the amount that reacted with the substance being analysed.
- Follow the reaction ratio. Convert to the amount, mass or concentration requested.
- Check the final unit and significant figures. A percentage above 100% nearly always signals an earlier error.
The later titration measures excess reagent. It must usually be subtracted from the amount originally added.
When a table is provided, use the concordant accurate titres to calculate the mean. Do not average every result automatically.
Year 13 redox back titrations
In a redox back titration, one or more later redox reactions measure the excess reagent. Calculate the original amount, find what remained, subtract, then use the equations to reach the substance being analysed.
Year 12 mode keeps redox switched off by default. Students who want an extension can still select mixed or redox-only questions deliberately.
Why back titration is used
A direct titration may be unsuitable when a solid reacts slowly, is insoluble, or does not give a sharp endpoint. A measured excess of reagent is allowed to react completely, then the unused excess is determined by a second titration.